We propose to investigate quantitatively adenosine, deoxyadenosine and adenine transport and metabolism in human erythrocytes and mouse and rat lymphocytes. The kinetics of adenosine and adenine transport will be measured in deoxycoformycintreated, ATP(PRPP)-depleted cells by rapid kinetic techniques. We will also determine the kinetic parameters for adenosine phosphorylation and deamination and adenine phosphoribosylation in whole cells and cell lysates and quantitate intracellular and extracellular concentrations of substrates and metabolites. Adenosine plays an important regulatory role in several human tissues by interacting with adenylate cyclase-coupled cell surface receptors. The source of the extracellular adenosine has not been identified, and we deem it possible that red cells play a contributory role. Red cells have also been implicated in the transfer of purines from the liver to other tissues, particularly lymphoidal cells, that are deficient in purine biosynthesis. Red cells themselves also need to salvage adenosine or adenine from the circulation for the maintenance of ATP levels. The metabolic pathways of purine metabolism in human red cells have been delineated, but little is known of the interaction between the pathways and transport as a function of adenosine concentration or the mode of transfer of purines between tissues. Our proposal promises to yield information on these points. The results also promise to contribute to an understanding of the basis of adenine nucleotide changes in red cells and lymphocytes in patients with adenosine deaminase deficiency.